Online Tutorials: Optical Filters
Filters are a specifically designed optical material (mainly glass but sometimes plastic) that either absorb and remove selected wavelengths of light or add special effects such as soft focus, extra magnification, starbursts or multiple images.
There are two main categories of filter. The first category represents technical filters, which add special effects or modify optical characteristics. The second simply alters the aesthetics of the image.
A filter with a grey appearance that rotates in its mount so you can block polarized light. It gives a blue sky a rich deep colour and is used to reduce reflections in water or other non-metallic materials. This filter comes in two varieties, linear (manual focus cameras) and circular (for autofocus cameras). If you look at the two cloudy blue sky pictures, the first image looks flat whereas the second image is more vibrant and defined.
A filter range that can give a dreamy look to your image and softens the contrasts and contours of your subject. Often used in portrait and some landscape photography. If you look at these two images, the second image is slightly softer than the first.
Skylight and UV
These filters reduce the haze levels and UV light exposed to your media. Some people use them to protect the front of their lenses as these filters are quite cheap and easy to replace. The advantage of these filters is noticeable mainly at high altitude.
These filters are used to correct colour imbalance in your image. Filters of this type come in various densities of red, green, blue, yellow, magenta and cyan. Some of the extreme colours are used in black and white photography.
ND filters shade the amount of light entering the camera, allowing a longer exposure to be made. ND filters are often used in macro work, as they allow wide apertures to be used, reducing the depth of field.
Grad filters are a hybrid of the colour compensating and ND filters, but the density of colour gradually increases towards the top of the filter. Particularly useful in landscape photography when compensating for a dark foreground and light sky.
Warming filters reduce the blue cast in photographs taken in the midday sun by giving the image a golden glow. Also useful in portrait work.
Cooling filters do the exact opposite of warming filters, emphasising the blue light that is weaker in the morning and evening light.